1. Field of the Invention
The present invention relates to a focusing device, and more particularly to a focusing device capable of setting a focusing area according to the result of detecting a target subject. The present invention further relates to an image-capturing apparatus provided with such a focusing device.
2. Description of the Related Art
Autofocus control that utilizes a subject detection function for detecting the face of a human figure, a moving subject, or the like is known to be conventionally used in image-capturing apparatuses as typified by digital cameras. This is a technique for focusing on a target subject such as the face of a human figure by detecting the target subject from a captured image, setting a focusing area in a part of the detected target subject, and performing focus control (see Japanese Patent Laid-Open No. 2003-107335).
If the target subject cannot be detected with such autofocus control, focus control can conceivably be performed by setting a focusing area in an area that is generally considered highly probable to include a target subject, such as the center of the image.
When shooting a movie or the like, there are situations where continuous autofocus (AF) that continuously performs control to focus on a set focusing area is performed. If the above-described autofocus control, which utilizes the detection of a target subject, is applied to the continuous AF, although no problem arises when a target subject is detected continuously, a problem arises in a case such as where the target subject cannot be detected.
In other words, when a target subject is detected, a focusing area is set in a part of the target subject, whereas when the target subject can no longer be detected, the focusing area is set in the center area of the image. Accordingly, the focusing area frequently switches between the target subject area and the center area of the screen, so when the target subject is not in the center of the screen, the in-focus position changes at a very rapid pace.
This condition shall be described with reference to FIGS. 8A to 8D.
When photographing a scene in which a target subject (a person's face, in this case) is not in the center area of the screen, as shown in FIG. 8A, if the target subject 810 is detected, a focusing area 801 is set in a position corresponding to the position of the target subject.
When the detection of the target subject (i.e., the detection of the face, in this case) fails after the target subject 810 has turned his/her face to a side or the like, a focusing area 802 is set in the center of the screen. Generally, when no target subject is present in the center of the screen, the in-focus position changes. Particularly, when photographing a scene containing a distant landscape in the background, the in-focus position changes significantly.
If the target subject then turns back to the front again, the target subject is detected, and the display is returned to the state shown in FIG. 8A. Such change of the in-focus position between the target subject and the subject that is in the background causes a problem that flicker occurs in the image, which is distracting for the user.
To solve this problem, a remedy has been conceived in which the position of the target subject is predicted with some kind of method even when the target subject can no longer be detected, and a focusing area 803 is set in the predicted position of the target subject as shown in FIG. 8C.
However, even if the position of the target subject can be predicted, it is difficult to accurately predict the position of the target subject continuously. If a focusing area 804 is set in an erroneously predicted position of the target subject as shown in FIG. 8D, there is no way to solve the problem.